Nickel alloy target including a secondary metal

ABSTRACT

A target includes nickel and a secondary metal. The secondary metal has a volume percentage between about 1 percent and about 10 percent. The secondary metal has a density between about 5,000 kg/m 3  and about 15,000 kg/m 3 .

BACKGROUND

Complementary metal-oxide-semiconductor (CMOS) devices comprise sourceregions, drain regions, and gate electrodes, which are often formed ofsilicon-containing materials. To reduce the contact resistance betweenthe silicon-containing source/drain regions and the silicon-containinggate electrodes, metal silicides may be formed atop the source/drainregions and the gate electrodes prior to the formation of various metallayers comprising conductive interconnect lines and vias. The mostcommonly used metal silicides are nickel silicide and cobalt silicide,typically formed by a self-aligned silicide (salicide) process.

In a salicide process, a thin layer of metal is blanket deposited byphysical vapor deposition (PVD) over a semiconductor wafer, specificallyover exposed source/drain regions and gate electrodes. The wafer is thensubjected to one or more annealing steps, for example, at a temperatureof 250° C. or higher. The annealing process causes the metal toselectively react with the exposed silicon of the source/drain regionsand the gate electrodes, thereby forming metal silicide regions. Theprocess is referred to as a self-aligned silicidation process becausethe silicide layer is formed where the metal material directly contactsthe silicon source/drain regions and the gate electrode. Following theformation of the silicide regions, the un-reacted metal is removed. Aninterconnect process is then performed to provide conductive paths, suchas by forming via holes through a deposited interlayer dielectric andfilling the via holes with a conductive material, e.g., tungsten orcopper.

For sub-65 nm technologies, nickel is widely used to form silicides. Aproblem of the nickel silicide is its poor thermal stability, and thetendency of forming agglomeration. The resistivity of the resultingsilicide is increased as a result of the agglomeration. To improve thethermal stability of nickel silicides, platinum may be added to thenickel silicide. To add platinum, the target that is used in the PVD isadded with platinum, which may have a percentage between about 5 percentand about 10 percent. The improvement in the thermal stability of thesilicides as a result of adding platinum, however, is still notsatisfactory, and the thermal stability of the silicides needs to beimproved further.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantagesthereof, reference is now made to the following descriptions taken inconjunction with the accompanying drawings, in which:

FIG. 1 illustrates a perspective view of a target in accordance with anembodiment, which may be using in a physical vapor deposition (PVD)tool;

FIG. 2 schematically illustrates the PVD tool and the target installedtherein;

FIGS. 3 an 4 are cross-sectional views of intermediate stages in themanufacturing of silicide regions of a metal-oxide-semiconductor (MOS)device in accordance with an embodiment; and

FIG. 5 illustrates experiment results, wherein the sheet resistances ofdifferent alloys are illustrated as a function of annealingtemperatures.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussedin detail below. It should be appreciated, however, that the embodimentsprovide many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative, and do not limit the scope of the disclosure.

A target for a physical vapor deposition (PVD) process and the silicidesformed using the target are provided in accordance with an embodiment.The variations of the embodiment are then discussed. Throughout thevarious views and illustrative embodiments, like reference numbers areused to designate like elements.

FIG. 1 illustrates a schematic perspective view of target 20, which maybe used for PVD processes. In an embodiment, target 20 has a circulartop-view shape (or any other applicable shape such as square andrectangle), and may have diameter D between about 15 inches and about 20inches. It is realized, however, that the dimensions recited throughoutthe description are merely examples, and may be changed.

Target 20 may include nickel, with the volume percentage of nickel intarget 20 being greater than about 90 percent. The volume percentage ofnickel may also be between about 90 percent and about 99 percent. Inaddition, target 20 includes an additional metal(s) (referred to as asecondary metal hereinafter). The secondary metal may have densitiesranging from about 5,000 kg/m³ to 15,000 kg/m³. In addition, thesecondary metal may have a diffusivity that is higher than thediffusivity of nickel, wherein the diffusivity is measured as thediffusivity of the secondary metal in silicon. With a high diffusivity,and hence smaller chance to form agglomeration, the secondary metal hasgood thermal stability during silicide processes, in which the metallayers formed using target 20 react with silicon to form silicideregions.

In some embodiments, the secondary metal includes a metal selected fromthe group consisting essentially of zinc, molybdenum, ruthenium, andcombinations thereof. Target 20 may thus be an alloy of nickel and oneor more of zinc, molybdenum, and ruthenium. The density of nickel is8,800 kg/m³. The density of zinc is 7,135 kg/m³. The density ofmolybdenum is 10,188 kg/m³. The density of ruthenium is 12,370 kg/m³.The secondary metal in target 20 may have a volume percentage betweenabout 1 percent and about 10 percent. In the case a single one (but notall) of zinc, molybdenum, and ruthenium is included in target 20, thesingle secondary metal has a volume percentage between about 1 percentand about 10 percent, or between about 4 percent and about 6 percent. Inthe embodiments wherein more than one of zinc, molybdenum, and rutheniumis used in target 20, the secondary metals have a total volumepercentage between about 1 percent and about 10 percent, or betweenabout 4 percent and about 6 percent.

FIG. 2 illustrates a schematic cross-sectional view of production tool30, which may be a PVD tool, although production tool 30 may also beused for other deposition methods. Production tool 30 includes chamber32 that is capable of being vacuumed, so that a vacuum environment isgenerated in chamber 32. Target 20 is installed in chamber 32. Wafer 34is placed on pedestal 36, which may be an electrostatic chuck (E-Chuck)configured to hold wafer 34 in place. Wafer 34 may be a semiconductorwafer for forming integrated circuits. In the PVD process, the metalatoms in target 20 may be sputtered off, and deposited on the surface ofwafer 34. The energy source for sputtering target 20 may be a DC voltagesource 35, although a radio frequency (RF) energy source may also beused.

FIGS. 3 and 4 are cross-sectional views of intermediate stages in asilicidation process performed on wafer 34 as shown in FIG. 2. Referringto FIG. 3, wafer 34 comprises metal-oxide-semiconductor (MOS) device 40,which may be formed on silicon-containing substrate 42.Silicon-containing substrate 42 may be a bulk silicon substrate, or mayhave a silicon-on-insulator structure. Source and drain regions 44(referred to as source/drain regions hereinafter) are formed, and maycomprise silicon. Source and drain regions 44 may, or may not, comprisenickel and/or the secondary metal. MOS device 40 may be adjacent toisolation regions 46, which may be shallow trench isolation (STI)regions. A gate stack comprising gate dielectric 48 and gate electrode50 is formed over substrate 42. Gate electrode 50 may be a metal gate ora polysilicon gate.

Using production tool 30 as in FIG. 2, metal layer 52 (FIG. 3) may bedeposited on MOS device 40, wherein metal layer 52 is in contact withsource and drain regions 44. The materials of metal layer 52 aresputtered off from target 20 (FIG. 2), and hence metal layer 52 includesnickel and the secondary metal. In addition, metal layer 52 may have acomposition (the percentages of nickel and the secondary metal) close tothe composition of target 20, although the compositions of nickel andthe secondary metal may be slightly different from that of target 20.

Referring to FIG. 4, an annealing is performed, forming source/drainsilicide regions 54 over and contacting source/drain regions 44. In theembodiments wherein gate electrode 50 is a polysilicon gate, gatesilicide 56 is also formed. The annealing may be performed at atemperature over about 400° C., although a lower temperature may beused, providing the quality of the resulting silicide regions is notcompromised. The annealing process may be performed using thermalannealing, flash annealing, laser annealing, and the like. In anexemplary embodiment, the annealing process comprises two steps. Thefirst step includes a first annealing at a relatively low temperature.In the first step, a portion of metal layer 52 (FIG. 3) reacts withsilicon to form a silicide. This silicide typically has a higherresistivity than in the structure as shown in FIG. 4. Un-reacted metallayer 52 is then removed. The second step includes a second annealing toconvert the high-resistive silicide to a low-resistive silicide. In anexemplary embodiment, the first annealing is performed at about 300° C.to about 400° C., while the second annealing is performed at about 700°C.

It is observed that in the silicidation process, although silicon isadded into nickel and the secondary metal, the addition of silicon doesnot affect the relative ratio of nickel to the secondary metal.Alternatively stating, in silicide regions 54 and 56, the volumepercentage of nickel among nickel and the secondary metal remains thesame as the volume percentage of nickel in metal layer 52. The volumepercentage of nickel among nickel and the secondary metal may beexpressed as:PNi=(VNi/(VNi+VSM))*100%  (Eq. 1)Wherein PNi is the volume percentage of nickel among nickel and thesecondary metal, VNi is the total volume of nickel in the respectivesilicide regions 54 and 56, and VSM is the total volume of the secondarymetal.

Similarly, in silicide regions 54 and 56, the volume percentage of thesecondary metal among nickel and the secondary metal remains the same asthe volume percentage of the secondary metal in metal layer 52. Thevolume percentage of the secondary metal among nickel and the secondarymetal may be expressed as:PSM=(VSM/(VNi+VSM))*100%  (Eq. 1)wherein PSM is the volume percentage of the secondary metal among nickeland the secondary metal. Accordingly, in silicide regions 54 and 56, thevolume percentage of nickel among nickel and the secondary metal may bebetween about 90 percent and about 99 percent, while the volumepercentage of the secondary metal among nickel and the secondary metalmay be between about 1 percent and about 10 percent.

The composition of silicide regions 54 and 56 may also be expressed asSi_(x)Ni_(y)M_(z), wherein letter “M” represents the secondary metal,and letters “x,” “y,” and “z” represent the volume percentages ofsilicon, nickel, and the secondary metal, respectively. In anembodiment, ratio z/x is between about 0.005 and about 0.1.

After the formation of silicide regions 54 and 56, the remainingcomponents of MOS device 40 are formed. The formation process includesforming contact etch stop layer (CESL) 60 over silicide regions 54 and56, forming inter-layer dielectric (ILD) 62 over CESL 60, formingcontact openings (occupied by contact plugs 64) in ILD 62 and CESL 60,and filling the contact openings with a metallic material such astungsten to form contact plugs 64.

In the embodiments, due to the addition of the secondary metal, theresulting silicide regions 54 and 56 may have a significantly improvedthermal stability at temperatures higher than about 600° C. FIG. 5illustrates experimental results, wherein the sheet resistances ofvarious sample silicide regions are illustrated. The samples are formedon silicon wafers. The experimental results indicate that when theannealing temperatures are higher than 600° C., the silicide regionsformed using nickel and the secondary metal (comprising zinc,molybdenum, or ruthenium) have sheet resistances significantly lowerthan the silicide region formed by adding other metals such as tantalum,titanium. Especially, when zinc is added into nickel, the resultingnickel-and-zinc-containing silicides, when annealed at 700° C., have asheet resistance substantially equal to or smaller than the sheetresistances of all other silicides that are formed under differenttemperatures ranging from 50° C. to 700° C. This indicates that at 700°C., no agglomeration is formed in the silicides comprising nickel andzinc. Furthermore, under scanning electron microscope (SEM), thesilicide regions formed with zinc, molybdenum, or ruthenium added (to 5percent) also show that substantially no agglomeration is formed.

In accordance with embodiments, a target includes nickel and a secondarymetal. The secondary metal has a volume percentage between about 1percent and about 10 percent. The secondary metal has a density betweenabout 5,000 kg/m³ and about 15,000 kg/m³.

In accordance with other embodiments, a device includes a substrate anda MOS device. The MOS device includes a gate dielectric over thesubstrate, a gate electrode over the gate dielectric, a source/drainregion adjacent the gate dielectric, and a source/drain silicide overand contacting the source/drain region. The source/drain silicideincludes nickel and a secondary metal, wherein the secondary metal has adensity between about 5,000 kg/m³ and about 15,000 kg/m³.

In accordance with yet other embodiments, a PVD tool includes a chambercapable of being vacuumed. A target is installed in the chamber. Thetarget includes nickel and a secondary metal selected from the groupconsisting essentially of zinc, molybdenum, ruthenium, and combinationsthereof. The PVD tool further includes a pedestal configured to hold asemiconductor wafer thereon

In accordance with yet other embodiments, a method includes forming aMOS device, wherein the step of forming the MOS device includes forminga gate dielectric over a substrate; forming a gate electrode over thegate dielectric; and forming a source/drain region adjacent the gatedielectric. The method further includes, in a production tool,depositing a metal layer over the MOS device, wherein the metal layercontacts the source/drain region. A target in the production tool andused in the step of depositing includes nickel and a secondary metal,which is selected from the group consisting essentially of zinc,molybdenum, ruthenium, and combinations thereof. An annealing is thenperformed to react the metal layer with the source/drain region to forma source/drain silicide region.

Although the embodiments and their advantages have been described indetail, it should be understood that various changes, substitutions andalterations can be made herein without departing from the spirit andscope of the embodiments as defined by the appended claims. Moreover,the scope of the present application is not intended to be limited tothe particular embodiments of the process, machine, manufacture, andcomposition of matter, means, methods and steps described in thespecification. As one of ordinary skill in the art will readilyappreciate from the disclosure, processes, machines, manufacture,compositions of matter, means, methods, or steps, presently existing orlater to be developed, that perform substantially the same function orachieve substantially the same result as the corresponding embodimentsdescribed herein may be utilized according to the disclosure.Accordingly, the appended claims are intended to include within theirscope such processes, machines, manufacture, compositions of matter,means, methods, or steps. In addition, each claim constitutes a separateembodiment, and the combination of various claims and embodiments arewithin the scope of the disclosure.

What is claimed is:
 1. A target comprising: nickel and a secondarymetal, wherein the secondary metal has a volume percentage between about1 percent and about 10 percent, and wherein the secondary metal has adensity between about 5,000 kg/m³ and about 15,000 kg/m³.
 2. The targetof claim 1, wherein the secondary metal is selected from the groupconsisting essentially of zinc, molybdenum, ruthenium, and combinationsthereof.
 3. The target of claim 2, wherein the secondary metal compriseszinc.
 4. The target of claim 2, wherein the secondary metal comprisesmolybdenum.
 5. The target of claim 2, wherein the secondary metalcomprises ruthenium.
 6. The target of claim 1, where the nickel in thetarget has a volume percentage greater than about 90 percent.
 7. Thetarget of claim 1 being configured to be used in a physical vapordeposition (PVD) tool, wherein the PVD tool comprises: a chamber capableof being vacuumed, wherein the target is capable of being installed inthe chamber; and a pedestal configured to hold a semiconductor waferthereon.